I think that people should prepare couples that things get really tough when you have a baby. It's really common to feel almost like you hate each other.
However, when he is starting to abuse drugs and then tries to shift the blame to you... well, that's no fair to you or your child.
I suggest counselling for you as a couple and individually (really helped me after my DD was born) but please don't make your baby grow up with an addict for a parent. Either he gets clean or he has supervised visits (or no visits if you think that he would be a danger)
He HAS TO know that it is not ok to use drugs and parent... Your baby deserves better than that.